WBBSE Solutions For Class 7 Geography Chapter 1 Earths Revolution Topic A Revolution Of The Earth

WBBSE Chapter 1 Earths Revolution Topic A Revolution Of The Earth Long Question And Answers

Question 1. What is an ellipse? How different is it from a circle?
Answer:

Ellipse:

An ellipse has two axes, the major axis AB and the minor axis CD (see figure), which intersect at the center O. In an ellipse, there are two foci, F and F1, equidistant from the center ‘O’.

1. Here, AB And CD = Two axis of equal length
2. O = Centre

1. Here, AB = Major Axis CD Minor Axis
2. O = Centre
3. F and F1 = Two Foci

Read And Learn Also WBBSE Solutions For Class 7 Geography

The differences noticed between a circle and an ellipse from the figure are-

WBBSE Class 7 Earth’s Revolution

Question 2. What are the distinct characteristics of the Earth as it revolves around the Sun?
Answer:

Characteristics of the Earth as it revolves around the Sun:

As the Earth revolves around the Sun, the following distinct characteristics are observed-

1. Elliptical orbit: The Earth moves around the Sun in a fixed elliptical path known as the Earth’s orbit.

2. Counter-clockwise movement: The Earth moves around the Sun along an elliptical path in an anti-clockwise direction.

3. Speed: The Earth revolves around the Sun at a speed of 30 km per second.

WBBSE Class 7 Geography Notes	WBBSE Solutions For Class 7 History
WBBSE Solutions For Class 7 Geography	WBBSE Class 7 History Multiple Choice Questions
WBBSE Class 7 Geography Multiple Choice Questions	WBBSE Solutions For Class 7 Maths

 

Question 3. What do you mean by the revolution of the Earth?
Answer:

Revolution of the Earth:

The Earth’s revolution refers to its movement around the Sun along a defined elliptical orbit. It takes 365 days, 5 hours, 48 minutes and 46 seconds or 1 year for the Earth to complete one revolution around the Sun.

The speed of the revolution of the Earth is 107000 km/h or 30 km/second.

Question 4. What are the types of the Earth’s motion?
Answer:

The Earth does not remain static in space, it is always in motion.

The Earth’s movement is of two types-

1. Rotation,
2. Revolution.

1. Rotation:

Rotation is the motion of the Earth on its own axis. It takes 24 hours for the Earth to complete one rotation and causing the occurrence of day and night.

2. Revolution:

Revolution is the motion of the Earth around the Sun. It takes 365 days, 5 hours, 48 minutes, and 46 seconds to complete one revolution.

Question 5. Discuss the features of the Earth’s orbit.
Answer:

Features of the Earth’s orbit:

The path along which the Earth revolves around the Sun is called its orbit. Its features are as follows-

1. It is elliptical in shape.
2. Its circumference is about 940 million km.
3. The Sun lies at the focus of the orbit.
4. The plane on which the orbit lies is called the orbital plane.
5. The speed at which the Earth revolves around the Sun along its orbit is approximately 30 km/s.
6. The Earth revolves around the Sun along this path from west to east in 365 days 5 hours 48 minutes 46 seconds.

 

Question 6. What are the three universal ways of determining time?
Answer:

Three ways of determining time are as the time lag. Therefore, in every 4 years follows-

1. On the basis of rotation:

Every 24 hours gives us a new day and a night. We consider 24 hours to be 1 day and break it into 24 parts.

2. On the basis of revolution:

The Earth takes 365 days to complete 1 revolution around the Sun. Considering 365 days to be 1 year we can determine time.

3. On the basis of lunar month:

The Moon, the only natural satellite of the Earth takes about 28 days (27 days 3 hours) to complete one revolution around the Earth. These 28 days are considered to be 1 month, though we have months of 30 and 31 days.

Question 7. What is Aphelion?
Answer:

Aphelion:

• Aphelion is the position when the Earth is farthest from the Sun.
• The Earth reaches its Aphelion position when the northern hemisphere July when it is about 15 crore 20 lakh km away from the Sun.

The word Aphelion is derived from the Greek words ‘apo’ meaning away or, apart, and ‘helios’ meaning the Greek God of the Sun.

Question 8. What is the position of the Earth’s axis as it moves around the Sun?
Answer:

As the Earth moves around the Sun, its axis makes an angle of 66½° with the orbital plane.

This tilt in the axis is responsible for the orientation of the North Pole towards the Pole Star and the South Pole towards Hadley’s Octant. The angular tilt of the Earth’s axis is fixed irrespective of its position.

WBBSE Chapter 1 Earths Revolution Topic A Revolution Of The Earth Short Question And Answers

Question 1. Explain the Law of Gravitation as per Newton. Does this work in outer space too?
Answer:

Law of Gravitation as per Newton:

• Newton’s Law of Gravitation states that any two bodies in the universe attract each other with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
• This law was discovered by Newton in the year 1867. Yes, this Law of Gravity is applicable in outer space too.

Question 2. Write a brief note on the Milky Way.
Answer:

Milky Way:

• The Milky Way is the galaxy that contains our solar system. Its name ‘milky’ is derived from its appearance as a dim glowing band arching across the night sky in which individual stars cannot be distinguished.
• The diameter of the Milky Way is about 0.1 million light-years i.e. light would take 0.1 million years to travel from one end to the other.

Question 3. What is escape velocity? If an object is thrown upwards at a velocity of 11.2 km per second, it does not fall back to the surface. Why?
Answer:

Escape velocity:

• Escape velocity is the velocity at which an object needs to travel to break free from a planet’s gravitational field and leave it without further propulsion.
• The escape velocity of an object from the Earth’s surface is 11.2 km per second.
• However small or big an object may be, the escape velocity is the same for all i.e. it does not depend on the mass of the object.

Question 4. Define leap year. or, Why does the month of February have 29 days after every 4 years? or, What is the reason behind the addition of a day in the calendar in every 4 years?
Answer:

Leap year:

• The period of time taken by the Earth to complete one revolution around the Sun (365 days, 5 hours, 48 minutes, and 46 seconds) is known as a solar year.
• For ease in calculation, this time is taken as 365 days and 6 hours (5 hours, 48 minutes, 46 seconds).
• The extra 6 hours of each year is added after every 4 years to the month of February (6 x 4 = 24 hours or 1 day) to adjust February has 29 days. This year with 366 days is known as a leap year.

Question 5. Identify the leap years- 2004, 2000, 2012, 1900, 2013, 2100.
Answer:

Year	Leap Year
	Yes	No
2004	Yes	–
2000	Yes	–
2012	Yes	–
1900	–	Yes
2013	–	Yes
2100	–	Yes

 

Question 6. Differentiate between the orbit and orbital plane of the Earth.
Answer:

The differences between the orbit and the orbital plane of the Earth are-

Question 7. Why is the heat produced by vertical sun rays more intense than that of oblique sunrays?
Answer:

The reasons for why the heat produced by vertical sun rays is more are as follows-

1. In comparison to vertical sun rays, oblique sunrays travel a longer distance through the atmosphere and thus, produce
   less heat.
2. Since the oblique rays travel a longer distance through the atmosphere, part of it gets absorbed by the surface of the water vapour droplets and minute dust particles in the atmosphere. Since the vertical rays travel a shorter distance lesser part of it gets absorbed by the atmospheric components.
3. The vertical sunrays are concentrated on a smaller portion of the Earth’s surface and so the heat produced is much more than that by the oblique ones.

Question 8. What is the reason behind the seasonal changes on the Earth’s surface?
Answer:

The Earth’s seasons are not caused by the distance from the Sun but the tilt in the Earth’s axis.

Due to this tilt different parts of the globe are oriented toward the Sun at different times of the year resulting in differential heating of the land surface. Therefore, we experience seasonal changes.

Question 9. During winter, in the northern hemisphere, the Sun appears to be bigger in size. Why?
Answer:

• The Sun is positioned at the center of the elliptical orbit of the Earth.
• The Earth-Sun distance is not constant and varies throughout the year.
• On 3 January when it is winter in the northern hemisphere, the Earth reaches a point nearest to the Sun (Sun-Earth distance is 14 crore 70 lakh km).
• Therefore the Sun appears bigger in size when seen from the Earth.

Question 10. What is the role of the daily motion of the Earth in determining time in hours, minutes, and seconds?
Answer:

• The geoid-shaped Earth takes 24 hours to complete one full rotation on its own axis from west to east.
• Every 1° rotation takes 4 mins (i.e. 360° x 4 minutes = 24 hours).
• Thus we divide each day into 24 parts and consider each part to be an hour. Further, 1 hour is divided into 60 minutes and 1 minute is divided into 60 seconds.
• In this manner, we can determine the time at a place in hours, minutes, and seconds.

Question 11. What happens if you drop a ball from your hand?
Answer:

• If we drop a ball from our hand, it will fall on the ground. This is because the Earth attracts every object towards its center.
• Thus, we do not fall off from the surface of the Earth and stay on it. This attraction is known as the gravitational force.

Question 12. What is the Earth attracted to?
Answer:

Earth attracted to:

• According to the law of gravity, every object in this universe attracts other objects.
• Likewise, the Earth also attracts any object closer or farther away from it and also gets attracted to any such.
• The heaviest object closest to the Earth is the Sun.
• Compared to the Earth the Sun is 13 lakh times bigger and thus the Earth is always attracted to it.

Question 13. If we drop a ball from our hand, it will fall on the ground. The Earth is like a heavy ball and also has chance of falling. In which direction and why will it fall? Or, The Earth is also a heavy sphere. Suppose the Earth also falls like a ball, what will happen to us?
Answer:

The Earth is constantly acted upon by the Sun’s gravity. If at all the Earth’s motion stops, then it will fall on the Sun’s surface.

Question 14. What problems would we have had faced in the absence of the gravitational force?
Answer:

• Gravitational force is responsible for the presence of an atmosphere, water, humans, birds animals, etc. on the surface of the Earth.
• In the absence of gravitational force, these would not have had existed and the Earth would have been a lifeless planet.

Question 15. An apple falls on the Earth’s surface from a tree. Both the apple and the Earth have the gravitational force of their own by which they attract each other. Then why does the apple fall down on the Earth’s surface and not the other way around?
Answer:

• Objects with more mass have more gravity.
• As the mass of the Earth is many times greater than the mass of the apple, the force acting on the apple is far stronger than the force acting on the Earth.
• So the apple falls on the Earth and not the other way round.

Question 16. How does the Earth move smoothly around the Sun?
Answer:

• The Earth revolves around the Sun along a fixed elliptical path. An object requires a centripetal force to revolve around the Sun.
• This centripetal force is provided by the Sun itself, helping in the swift movement of the Earth along its path.

Question 17. If you place a small piece of paper on a ball and let it go after rotating it, the paper would fall off. Similarly, we reside on the Earth’s surface but don’t fall off. Why?
Answer:

• In the given example we saw that the ball did not have any gravitational force of its own due to which the piece of paper fell off from its surface.
• Our Earth has its own gravitational force that always attracts us downwards and hence, we do not fall off from its surface.

Question 18. What do you mean by rotation?
Answer:

Rotation:

• The spinning of the Earth on its own axis is termed as Earth’s rotation.
• The average rotation period of the Earth is 23 hours 56 minutes 4 seconds i.e. 24 hours.

Question 19. Why is the Earth’s revolution also called the annual motion of the Earth?
Answer:

• The Earth takes 365 days, 5 hours, 48 minutes, and 46 seconds to complete one revolution around the Sun.
• Since 365 days is taken to be 1 year the movement is also known as the annual motion of the Earth.

Question 20. What is the orbit of the Earth?
Answer:

Orbit of the Earth:

• The elliptical path along which the Earth revolves around the Sun is termed as the Earth’s orbit.
• The circumference of the orbit is about 940 million km.
• The Sun is positioned at the center or focus of the elliptical orbit.

Question 21. State Kepler’s first law.
Answer:

Kepler’s first law:

Kepler’s first law says, “Each planet revolves around the Sun in an elliptical orbit with the Sun at the focus of the ellipse.”

Question 22. What is Earth’s orbital plane?
Answer:

Earth’s orbital plane:

• The imaginary plane on which the orbit of the Earth is situated is known as the orbital plane of the Earth.
• This two-dimensional plane is elliptic in shape and prevents celestial bodies from bumping into each other.
• The center of the Sun and the center of the Earth are on the same orbital plane.

Question 23. What is Perihelion?
Answer:

Perihelion:

• Perihelion is the position when the Earth is nearest to the Sun. It occurs on 3 January every year and the Sun-Earth distance at this point is about 14 crore 70 lakh km.
• The word Perihelion is derived from the Greek words ‘peri’ meaning near and ‘helios’ meaning the Greek God of the Sun.

Question 28. One bucket of water warms up within half an hour if it is placed in the Sun at noon. When do you think we get more heat during that time?
At the time of sunrise
At noon when the Sun is overhead During sunset
At night after sunset
Answer:

At noon when the Sun is overhead.

Question 29. What is escape velocity?
Answer:

Escape Velocity:

• If an object is thrown upwards at a velocity of 11.2 km/sec, it will go past the Earth’s gravitational force and start revolving around it.
• This velocity is known as the object’s escape velocity in the case of the Earth.

Question 30. On 3 January, the Sun-Earth distance is minimum (14 crores 70 lakh km) as a result of which we should feel warmer but we normally feel cold. Why?
Answer:

• On 3 January, the southern hemisphere is tilted towards the Sun while the northern. hemisphere is tilted away from it.
• Due to this, the Sun’s rays fall vertically over the southern hemisphere and obliquely over the northern hemisphere and hence, we feel cold.

WBBSE Chapter 1 Earths Revolution Topic A Revolution Of The Earth Very Short Question And Answers

Question 1. Name the galaxy which contains the Sun and the entire solar system.
Answer: Milky Way.

Question 2. Where is the Sun located in the solar system?
Answer: Centre.

Question 3 What is the diurnal motion of the Earth on its own axis called?
Answer: Rotation.

Question 4 What is the name for the Earth’s movement around the Sun in 365 days?
Answer: Earth’s revolution.

Question 5. What is the term for the velocity at which an object thrown upwards from the Earth manages to escape the gravitational force of the Earth?
Answer: Escape velocity.

Question 6. What is the elliptical path on which the Earth moves around the Sun called?
Answer: Orbit.

Question 7. What is the line imagined to join the Poles of the Earth known as?
Answer: Earth’s axis.

Question 8. What is the name of the position attained on 3 January at which the Sun-Earth distance is minimum?
Answer: Perihelion.

Question 9. What is the name of the position attained on 4 July at which the Sun-Earth distance is maximum?
Answer: Aphelion.

Question 10 What is the period of 28 days during which the Moon completes one revolution around the Earth called?
Answer: Lunar month.

Question 11 What is a year that is exactly divisible by four called?
Answer: Leap year.

Question 12 What is the year with 366 days and with 29 days in February called?
Answer: Leap Year.

Question 13. Mention the angle at which the Earth’s axis is tilted with respect to the orbital plane.
Answer: 66½°.

Question 14. Where on Earth are days and nights equal?
Answer: Equator.

Question 15. Name the planet whose axial line and orbital path are parallel to each other.
Answer: Uranus.

Question 16. Name the planet whose axis is perpendicular to the orbital plane.
Answer: Jupiter.

Question 17. Why is the axis of the Earth tilted? Or, Why does the axis of the Earth make an angle of 66% with its orbit?
Answer:

Scientists believe that during the formation of the Earth due to collision with several extraterrestrial elements the axis of the Earth got inclined at an angle of 662°.

Question 18. What is a lunar month?
Answer:

Lunar month:

The Earth’s satellite Moon revolves around the Earth in about 27% of days or 28 days (approx). This period is called a lunar month.

Question 20. What is a solar day?
Answer:

Solar day

Solar day refers to th:e interval between two successive returns of the Sun to the local meridian. The length of a solar day varies throughout the year.

Question 21. How will you identify a year as a leap year?
Answer:

A year can be termed a leap year only if it is completely divisible by 4. In the case of millennium years like 1600, 2000, 2400, and so on, if it is divisible by 400, it is a leap year.

Question 22. What do you know about the Earth’s axis?
Answer:

Earth’s axis:

The imaginary line that joins the North and the South Poles and passes through the center of the Earth is known as the Earth’s axis. It is tilted, making an angle of 66½° with the orbital plane.

WBBSE Chapter 1 Earths Revolution Topic A Revolution Of The Earth Fill In The Blanks

Question 1. The force of the Earth that holds us onto its surface is called _______.
Answer: Gravitational force

Question 2. The Sun is _______ lakh times bigger than the Earth.
Answer: 13

Question 3. The Sun is at the _______ of the solar system.
Answer: Center

Question 4. ‘The Earth revolves around the Sun’-this idea was first put forward by _______.
Answer: Kepler

Question 5. Earth’s orbital path is _______.
Answer: Elliptical

Question 6. The idea of a heliocentric universe was first put forward by _______.
Answer: Copernicus

Question 7. The Theory of Planetary Motion was first put forward by famous scientist _______.
Answer: Kepler

Question 8. _______ is a result of the Earth’s rotation.
Answer: Day and night

Question 9. Smaller objects that move in an orbit around a larger object obey Newton’s Law of _______.
Answer: Gravitation

Question 10. In the month of _______ the Sun comes closest to the Earth.
Answer: January

Question 11. The duration of the solar year is _______
Answer: 365 days 5 hours 48 minutes 46 seconds

Question 12. The solar day is computed by _______ of the Earth.
Answer: Rotational

Question 13. The Sun takes _______ minutes to apparently cross one degree of longitude.
Answer: 4

Question 14. The year with 366 days is a _______.
Answer: Leap year

Question 15. During winter, in the northern hemisphere, the Sun appears to be slightly _______ in size.
Answer: Larger

Question 16. In the northern hemisphere, the Sun appears to be slightly smaller in size during _______.
Answer: Summer

Question 17. The Earth’s axis oriented in the direction of the Pole Star makes an angle of _______ with the orbital plane.
Answer: 662°

Question 18. The position of the North Pole is determined by the position of the _______.
Answer: Pole Star

Question 19. The Pole Star is observed in the _______ part of the sky in Kolkata.
Answer: Northern

WBBSE Chapter 1 Earths Revolution Topic A Revolution Of The Earth True or False

Question 1. The Egyptians first applied the concept of leap year.
Answer: True

Question 2. The Earth’s orbital path is circular in shape.
Answer: False

Question 3. During the revolution, the Earth’s axis remains tilted at an angle of 652°.
Answer: False

Question 4. At Aphelion, the Sun-Earth distance is minimum.
Answer: False

Question 5. At Perihelion, the Sun-Earth distance is maximum.
Answer: False

Question 6. A year with 365 days, 5 hours, 48 minutes, and 46 seconds is considered to be a leap year.
Answer: False

Question 7. Escape velocity from the surface of the Earth is 11.7 km per hour.
Answer: False

Question 8. The year 2008 was a leap year.
Answer: True

Question 9. In the northern hemisphere during summer, the Sun appears to be smaller.
Answer: True

Question 10. Speed of revolution: 30 km/sec:: Escape velocity:_________.
Answer: 11.2 km/sec

Question 11. Aphelion : _________:: Perihelion: 3 January.
Answer: 4th July

Question 12. Aphelion: 15 crore 20 lakh km:: Perihelion: _________.
Answer: 14 crores 70 lakh km

Question 13. Near to the Sun : _________:: Far away from the Sun: July.
Answer: January

Question 14. Lunar month: 27% days:: Solar year: _________.
Answer: 365 days

WBBSE Chapter 1 Earths Revolution Topic A Revolution Of The Earth Match The Columns

1.

Answer: 1. D, 2. A, 3. C, 4. B

2.

Answer: 1. B, 2. C, 3. A, 4. D

3.

Answer: 1. B, 2. A, 3. D, 4. C

4.

Answer: 1. B, 2. A, 3. D, 4. C